1. The present invention relates in general to an in line microwave warming apparatus. More particularly, the present invention relates to a microwave warmer for blood and intravenously fed fluids. Even more particularly, the invention relates to an in line microwave warmer in combination with temperature detection apparatus preferably employing radiometric measurement of temperature.
2. Background Discussion
In the medical field there presently exists a number of applications requiring the warming of blood and in some instances, intravenously fed fluids. For example, in connection with cardiac surgery during extracorporal circulation (ECC) the patient is first cooled in order to slow metabolism and thereafter there is a requirement that the circulating blood be warmed. For a discussion of blood warming in association with cardiac surgery refer to the article "Heating Blood and Extracorporal Circulation with a High Frequency Electromagnetic Field: Effect of Microwaves on Blood" by J. Andre, R. Barthelemy, S. Lefeuvre, A. Priou and J. P. Morucci, appearing in "Biomedical Thermology", pages 257-268, Copyright 1982, Alan R. Liss, Inc., 150 5th Avenue, New York, N.Y., 10011.
The Biomedical Thermology article just referenced, employs a microwave heating unit but as indicated in the article, the electric field that is established is non uniform and thus the blood or other liquid is heated in an inhomogeneous manner.
Another medical application for the warming of blood or intravenous fluids is in a trauma situation. For example, heated intravenous fluids are useful in hyperthermic patients and in trauma patients requiring massive IV resuscitation. Clasically, hyperthermic patients are warmed either passively, if the hyperthermia is mild, or actively, if severe. In this connection the microwave heating of intravenous fluids is addressed in the article "Microwave Heating of Intraveneous Fluids" by John S. Anshus, Gerald L. Endahl and J. Lawrence Mottley.
It has furthermore been found that cardiac arrest may occur due to hyperthermia resulting from the rapid, massive transfusion of refrigerated blood. In this connection reference is made to an article relating to associated dangers of overwarming blood. This is the article "Danger of Overwarming Blood by Microwave" by James F. Arens and George L. Leonard, "Journal American Medical Association", November 15, 1971, volume 218, No. 7.
One common technique for warming blood is to pass the blood through plastic coils immersed in a warm water bath. Of course, this method has numerous drawbacks, one in particular being the slowness of operation.
Microwave heating has been employed in connection with the heating of blood and intravenous fluids. Typically, a standard microwave oven is used to warm the entire blood bag. This has not been proven successful basically because it is virtually impossible to achieve uniform heating of the blood or other liquid due to both the non uniform distribution of microwave energy within the oven and the inability, using microwaves, to heat at sufficient depths in a lossy material such as blood which has a high dielectric constant. Basically, hot spots develop causing significant blood damage. Again, in this regard refer to the previously mentioned Arens, et al article.
A further problem associated with heating the entire blood bag in a microwave oven, is the inability to monitor the temperature of the liquid particularly at depths.